In the technical field of semiconductor devices, transition metal-silicon compounds made of transition metal and silicon are widely used as electrode materials of devices made of silicon. A transition metal-silicon compound is also called a “transition metal silicide film” or “transition metal silicide” or a “transition metal-silicon compound.” The transition metal-silicon compound has excellent heat-resistant, oxidation resistant, corrosion resistant and electrically conductive characteristics. Furthermore, a producing process of a transition metal-silicon compound has high affinity to a manufacturing process of an LSI using silicon or the like.
On the other hand, research and development of devices made of germanium which excels silicon in electric characteristics are underway in recent years. Examples of types of devices include transistors, light-emitting devices, light-receiving devices and solar batteries. For the same reason as the reason for using a transition metal-silicon compound as an electrode material in a silicon device, a transition metal-germanium compound made of transition metal and germanium is expected as an electrode material of a germanium device. The transition metal-germanium compound is also called a “transition metal germanide film.”
When a transition metal film is deposited on a germanium substrate and the transition metal film is then subjected to heat treatment, transition metal reacts with germanium on the germanium surface, and it is possible to synthesize a compound of the transition metal and germanium. A type of the transition metal used in this method is, for example, nickel having a low melting point. On the other hand, it is known that tungsten which has a highest melting point among transition metals does not react with germanium even when subjected to heat treatment on the order of 900° C. close to the melting point of germanium (see Non Patent Literature 1).
As a thin film made up of a compound of tungsten and germanium, a tungsten film is known which contains germanium having a small germanium/tungsten composition ratio of 0.18 or less (see Non Patent Literature 2). This film is produced using a gas phase reaction film forming method using a material gas of GeH4 and WF6.
Regarding one cluster of tungsten germanium, a relationship between the composition ratio of W and Ge and the HOMO-LUMO (gap EHL between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)), theoretically calculated through a first principle calculation, is known (see Non Patent Literature 3).
The present inventors previously proposed a transition metal-silicon compound film relating to MSin (where, M: transition metal, Si: silicon, n=7 to 16) and proposed a semiconductor device using the transition metal-silicon compound film (see Patent Literature 1, Patent Literature 2).
Furthermore, the present inventors previously proposed a method for manufacturing a tungsten silicon compound film relating to MSin (where, M: tungsten, Si: silicon, n 12) (see Non Patent Literature 4).
As a result of search for prior documents related to the present application, a patent literature describing tungsten germanium (WGe) as an example of an electrode material for semiconductor devices was found (see Patent Literature 3).
Furthermore, the method for calculating an optical energy gap is known (see Non Patent Literature 5).